Breast cancer is a devastating affliction in Western Society. It is of high interest to quantify the expression of HER2/neu (a growth factor receptor), the estrogen receptor (ER), and the progesterone receptor (PR) in breast cancer tumors since HER2/neu expression is associated with high malignancy and because HER2Ineu, and ER are targets for anti-breast cancer therapies (Herceptin and tamoxifen, respectively). The presence or absence of PR is also helpful in diagnosing the sensitivity of a tumor to tamoxifen, since PR expression is dependent upon ER activity. The assay will quantify the populations of cells expressing HER2/neu, ER, and PR in the tumor sections obtained from biopsy material or surgical resection;each biomarker will be visualized in a separate optical channel and quantified on a cell by cell basis via fluorescence microscopy. The assay will feature hapten-coupled primary antibodies to HER2/neu, ER, and PR, and secondary reagents conjugated to quantum dots (ODoIS), which never photo bleach. Thus, slides prepared using the assay reagents and methods will be of archival quality. Furthermore, the ODot reagents and methods developed for this assay will be generally applicable for quantifying biomarkers in a wide variety of other tumor types, such as prostate cancer.